The current tendency is to provide preparations, in particular ophthalmic liquids, without preservative. The dispenser device must guarantee the sterility of the preparation throughout the working life of the bottle containing the liquid to be dispensed.
In an example, as described in document WO92/01625, such a dispenser device comprises a reservoir and a dispenser endpiece that is mounted on the reservoir and that is provided with a liquid dispenser orifice. The user applies pressure on the reservoir by deforming it, and, under the effect of the pressure, a drop is formed at the outlet of the dispenser orifice. Once the drop has been delivered, the user relaxes the pressure and the reservoir tends to return to its initial shape, thereby generating suction inside the reservoir. In order to compensate the suction and enable the reservoir to return to its initial shape, the endpiece of the device includes an air intake for admitting air into the reservoir. In order to ensure that the incoming air cannot contaminate the liquid contained in the reservoir, a hydrophobic filter is positioned in the air passage. The filter avoids micro-organisms and dust entering, while preventing liquid from exiting. The pore size of this type of filter is generally about 0.2 micrometers (μm), such that it prevents entry of most micro-organisms (e.g. Brevundimonas Diminuta bacteria which have a size of about 0.2 μm).
A problem with that type of device resides in the fact that it is very difficult to guarantee the integrity of used filters. In particular, it is difficult to test proper operation of the filter after it has been mounted on the endpiece, since the filter would then need to be tested in the presence of water or gas, thereby implying a risk of contamination or degradation during the test stage. Furthermore, none of the tests makes it possible to detect very small defects in the filter in a short period of time, compatible with manufacture at a very high rate.